Refrigerators having fresh food and freezer compartments have been known to include a door ajar alarm system for providing an audible or visual alarm when the door to either of the compartments has been open for a fixed period of time constituting the alarm delay period. By thus alerting the user, undesirable temperature conditions within the compartments may be avoided. It has been found, however, that the effect of an open compartment door on the compartment's temperature varies depending on the operating condition of the refrigerator. Under certain operating conditions the fixed alarm delay period may be too long so that undesirable temperature conditions may not be avoided by alerting the user with known door ajar alarm systems.
One operating condition during which an open compartment door has a great effect on the compartment's temperature is a defrost operation. During a defrost operation, defrost heat is being applied to the evaporator and the compressor cannot be energized to cool warm air which enters the compartment through an open door, so that undesirable temperature conditions are rapidly produced. It is, therefore, desirable to decrease the alarm delay period when the refrigerator is undergoing a defrost operation. Other operating conditions under which an open door rapidly produces undesirable temperatures, or temperature conditions, from which recovery is unusually slow may occur when either the fresh food or freezer compartment is at an abnormally high temperature or when the refrigerator is operating in a special cooling mode, for example, where the compartments are being cooled to the lowest practical temperature. Under such operating conditions the fixed alarm delay period of known systems, though suitable for normal operating conditions, may be too long to readily alert the user that the door should be closed.